Hello, I am going to build a mid 70's f-250 super cab shortbox f-250 4x4. My question is it better to find a long box 4x4 frame and shorten it or use a standard cab long box and lengthen it? I was kind of leaning towards lengthening a 67-77 standard cab frame so I could use the divorced t-case so my motor and trans options are greater. I am considering plundering a 95 powerstroke auto 2wd that I currently own for the motorand trans.
thank you

 

I'd say shorten - but depends on how you plan to do that. If you are just cutting 12" or so off the back, straight section - then by all means this is the better solution. If you mean shortening by taking a section of frame out of the middle and then putting back together - then I'd say it's a crapshoot between shortening or lengthening.

I have seen people modify these frames, and it all honesty 99% of them scare the crap out of me, and the other 1% still scare me a bit.

I'm not one that would ever really mess with a frame on one of these - aside from cutting 12" or so off the back (reducing the wheel base on a supercab to get it back to about 125"). I have seen people do "nice" work on the frame cuts by Z cutting them and also boxing the frame section that is where the weld/splice is, but for some reason it still scares me.

 

If you are very good with a torch and welder it doesn't matter if you shorten or lengthen if you are doing a middle section it can be done with no problems. I used to do that all the time on big trucks. You just make sure you measure 4times and cut once. Take your time, diamond plate your joints and be a damn good welder!! Good Luck

 

As 427 said, doesn't matter which way you go. All that matters is doing it right. Good, straight cuts, plate the joints, and quality welds.
I've stretched and shortened several trucks, some are hauling 50k plus loads daily.
If you stretch, try to find some actual frame rail to use as your filler. It's better than plain channel, and it'll flex rather than bend and rip.
just my .02 worth...

 

i would go with shortening,,,less fabricating kinda

 

How much do you need to change it?

A standard cab frame would be long enough for the supercab and shortbox, I would just move the spring hangers to adjust the wheelbase accordingly

You're going to run into problems with the shapes of the frame. The frame rises just behind the cab of a standard cab frame, which means you need a body lift under the front of a supercab to make it sit level.

 

You could build a NEW frame from firewall back outta box tubing, it would be alot stronger too, since these C channels flex quite a bit. Alot of fab work though.

 

my suggestion is if you do any frame chops in the middle i would box the frame from fire wall back, and if you can one piece box from front to back, which would be easier on a short box, due to the shorter length, that's the only way i would do it, plus it will look better and be stronger, boxing the cut section looks like a hack job, plus if you box the whole frame you not only strengthen the entire frame, but you reduce the stress on the welds, the frame is the back bone, trust me, you don't want to be going down a highway and have the frame snap, or snap under a load, it will not only destroy your truck but you could endanger lives on the road and possibly your own, so box it or don't bother, just my 2 cents, and its easy to route the lines still and will be a much safer and better looking result, i am not trying to discourage you, but make sure you do it right, for safety's sake

and i agree with chasetruck754 99 percent of these frame mods scare me, and even the 1 percent bother me, i just know there is lots of pressure on the frame and there is many safety concerns, but good luck with it

-Brent

 

I don't have much experiencn in making frames, but would it be possible or if fiesable to build a frame outta I-beams like they use in construction, I know it would be very heavy and big, but man would it be an indestructable frame!! Its just an idea I've been thinking of for awhile, and would like to know if it could work or not.

 

Anything is possible but you better have some very high fabrication skills

 

I would use the frame that matched the cab and shorten it to fit
boxing would be a major PITA as every crossmember would have to be worked around,
adding a formed C to fit inside the rail at the joint would be plenty strong
I suspect a good welded joint would be enough but the double thick section at the joint area would be piece of mind
I had a C30 chevy frame shortened as I described to replace my broken K10 shortbox frame

 

if you cut the frame, and weld it back at the joint, i would drill four holes, two about a foot behind and two about a foot in front of the weld, and use grade 8 bolts to secure a piece of half-inch flat stock to the side of the rail, so it adds strength, protection if the weld breaks, and is bolted into an area of the frame unaffected by the heat that changes the composition of the heat treated steel.

 

a larger piece of channel iron that fits snug over, or inside the frame would work too.

 

most of the new trucks dont have one piece frame rails, and i wouldnt be suprised if these didnt either. most are welded around the box/cab seperation, so doing it right isnt scarey at all.

 

im pretty sure that back in the day, they WERE one-piecers, but even if they werent, they were heat treated AFTER the assembly of the two (or more) peices. thus, cutting and welding will compromise the strength of the metal.